Role of LIMP-2 in the intracellular trafficking of ß-glucosidase in different human cellular models.

Acid ß-glucosidase (GCase), the enzyme deficient in Gaucher disease (GD), is transported to lysosomes by the lysosomal integral membrane protein (LIMP)-2. In humans, LIMP-2 deficiency leads to action myoclonus-renal failure (AMRF) syndrome. GD and AMRF syndrome share some clinical features. However, they are different from clinical and biochemical points of view, suggesting that the role of LIMP-2 in the targeting of GCase would be different in different tissues. Besides, the role of LIMP-2 in the uptake and trafficking of the human recombinant (hr)GCase used in the treatment of GD is unknown. Thus, we compared GCase activity and intracellular localization in immortalized lymphocytes, fibroblasts, and a neuronal model derived from multipotent adult stem cells, from a patient with AMRF syndrome, patients with GD, and control subjects. In fibroblasts and neuronlike cells, GCase targeting to the lysosomes is completely dependent on LIMP-2, whereas in blood cells, GCase is partially targeted to lysosomes by a LIMP-2-independent mechanism. Although hrGCase cellular uptake is independent of LIMP-2, its trafficking to the lysosomes is mediated by this receptor. These data provide new insights into the mechanisms involved in the intracellular trafficking of GCase and in the pathogeneses of GD and AMRF syndrome.

Cerebrospinal fluid lysosomal enzymes and alpha-synuclein in Parkinson's disease.

To assess the discriminating power of multiple cerebrospinal fluid (CSF) biomarkers for Parkinson's disease (PD), we measured several proteins playing an important role in the disease pathogenesis. The activities of ß-glucocerebrosidase and other lysosomal enzymes, together with total and oligomeric α-synuclein, and total and phosphorylated tau, were thus assessed in CSF of 71 PD patients and compared to 45 neurological controls. Activities of ß-glucocerebrosidase, ß-mannosidase, ß-hexosaminidase, and ß-galactosidase were measured with established enzymatic assays, while α-synuclein and tau biomarkers were evaluated with immunoassays. A subset of PD patients (n = 44) was also screened for mutations in the ß-glucocerebrosidase-encoding gene (GBA1). In the PD group, ß-glucocerebrosidase activity was reduced (P < 0.05) and patients at earlier stages showed lower enzymatic activity (P < 0.05); conversely, ß-hexosaminidase activity was significantly increased (P < 0.05). Eight PD patients (18%) presented GBA1 sequence variations; 3 of them were heterozygous for the N370S mutation. Levels of total α-synuclein were significantly reduced (P < 0.05) in PD, in contrast to increased levels of α-synuclein oligomers, with a higher oligomeric/total α-synuclein ratio in PD patients when compared with controls (P < 0.001). A combination of ß-glucocerebrosidase activity, oligomeric/total α-synuclein ratio, and age gave the best performance in discriminating PD from neurological controls (sensitivity 82%; specificity 71%, area under the receiver operating characteristic curve = 0.87). These results demonstrate the possibility of detecting lysosomal dysfunction in CSF and further support the need to combine different biomarkers for improving the diagnostic accuracy of PD.

Functional analysis of 11 novel GBA alleles.

Gaucher disease is the most frequent lysosomal storage disorder due to the deficiency of the acid ß-glucosidase, encoded by the GBA gene. In this study, we report the structural and functional characterization of 11 novel GBA alleles. Seven single missense alleles, P159S, N188I, E235K, P245T, W312S, S366R and W381C, and two alleles carrying in cis mutations, (N188S; G265R) and (E326K; D380N), were studied for enzyme activity in transiently transfected cells. All mutants were inactive except the P159S, which retained 15% of wild-type activity. To further characterize the alleles carrying two in cis mutations, we expressed constructs bearing singly each mutation. The presence of G265R or D380N mutations completely abolished enzyme activity, while N188S and E326K mutants retained 25 and 54% of wild-type activity, respectively. Two mutations, affecting the acceptor splice site of introns 5 (c.589-1G>A) and 9 (c.1389-1G>A), led to the synthesis of aberrant mRNA. Unpredictably, family studies showed that two alleles resulted from germline or 'de novo' mutations. These results strengthen the importance of performing a complete and accurate molecular analysis of the GBA gene in order to avoid misleading conclusions and provide a comprehensive functional analysis of new GBA mutations.

First pilot newborn screening for four lysosomal storage diseases in an Italian region: identification and analysis of a putative causative mutation in the GBA gene.

We report the first newborn screening pilot study in an Italian region for four lysosomal disorders including Pompe disease, Gaucher disease, Fabry disease and mucopolysaccharidosis type 1. The screening has been performed using enzymatic assay on Dry Blood Spot on filter paper. A total of 3403 newborns were screened. One newborn showed a reduction of ß-glucosidase activity in leucocytes. Molecular analysis revealed a status of compound heterozygous for the panethnic mutation N370S and for the sequence variation E388K, not yet correlated to Gaucher disease onset. The functional consequences of the E388K replacement on ß-glucosidase activity were evaluated by in vitro expression, showing that the mutant protein retained 48% of wild type activity. Structural modeling predicted that the E388K replacement, localized to a surface of the enzyme, would change the local charges distribution which, in the native protein, displays an overwhelming presence of negative charges. However, the newborn, and a 4 year old sister showing the same genomic alterations, are currently asymptomatic. This pilot newborn screening for lysosomal diseases appears to be feasible and affordable to be extended to large populations. Moreover other lysosomal diseases for which a therapy is available or will be available, could be included in the screening.

Nucleophosmin is overexpressed in thyroid tumors.

Nucleophosmin (NPM) is a protein that contributes to several cell functions. Depending on the context, it can act as an oncogene or tumor suppressor. No data are available on NPM expression in thyroid cells. In this work, we analyzed both NPM mRNA and protein levels in a series of human thyroid tumor tissues and cell lines. By using immunohistochemistry, NPM overexpression was detected in papillary, follicular, undifferentiated thyroid cancer, and also in follicular benign adenomas, indicating it as an early event during thyroid tumorigenesis. In contrast, various levels of NPM mRNA levels as detected by quantitative RT-PCR were observed in tumor tissues, suggesting a dissociation between protein and transcript expression. The same behavior was observed in the normal thyroid FRTL5 cell lines. In these cells, a positive correlation between NPM protein levels, but not mRNA, and proliferation state was detected. By using thyroid tumor cell lines, we demonstrated that such a post-mRNA regulation may depend on NPM binding to p-Akt, whose levels were found to be increased in the tumor cells, in parallel with reduction of PTEN. In conclusion, our present data demonstrate for the first time that nucleophosmin is overexpressed in thyroid tumors, as an early event of thyroid tumorigenesis. It seems as a result of a dysregulation occurring at protein and not transcriptional level related to an increase of p-Akt levels of transformed thyrocytes.

A proteomic approach to the bilirubin-induced toxicity in neuronal cells reveals a protective function of DJ-1 protein.

Unconjugated bilirubin (UCB) is a powerful antioxidant and a modulator of cell growth through the interaction with several signal transduction pathways. Although newborns develop a physiological jaundice, in case of severe hyperbilirubinemia UCB may become neurotoxic causing severe long-term neuronal damages, also known as bilirubin encephalopathy. To investigate the mechanisms of UCB-induced neuronal toxicity, we used the human neuroblastoma cell line SH-SY5Y as an in vitro model system. We verified that UCB caused cell death, in part due to oxidative stress, which leads to DNA damage and cell growth reduction. The mechanisms of cytotoxicity and cell adaptation to UCB were studied through a proteomic approach that identified differentially expressed proteins involved in cell proliferation, intracellular trafficking, protein degradation and oxidative stress response. In particular, the results indicated that cells exposed to UCB undertake an adaptive response that involves DJ-1, a multifunctional neuroprotective protein, crucial for cellular oxidative stress homeostasis. This study sheds light on the mechanisms of bilirubin-induced neurotoxicity and might help to design a strategy to prevent or ameliorate the neuronal damages leading to bilirubin encephalopathy.

APE1/Ref-1 interacts with NPM1 within nucleoli and plays a role in the rRNA quality control process.

APE1/Ref-1 (hereafter, APE1), a DNA repair enzyme and a transcriptional coactivator, is a vital protein in mammals. Its role in controlling cell growth and the molecular mechanisms that fine-tune its different cellular functions are still not known. By an unbiased proteomic approach, we have identified and characterized several novel APE1 partners which, unexpectedly, include a number of proteins involved in ribosome biogenesis and RNA processing. In particular, a novel interaction between nucleophosmin (NPM1) and APE1 was characterized. We observed that the 33 N-terminal residues of APE1 are required for stable interaction with the NPM1 oligomerization domain. As a consequence of the interaction with NPM1 and RNA, APE1 is localized within the nucleolus and this localization depends on cell cycle and active rRNA transcription. NPM1 stimulates APE1 endonuclease activity on abasic double-stranded DNA (dsDNA) but decreases APE1 endonuclease activity on abasic single-stranded RNA (ssRNA) by masking the N-terminal region of APE1 required for stable RNA binding. In APE1-knocked-down cells, pre-rRNA synthesis and rRNA processing were not affected but inability to remove 8-hydroxyguanine-containing rRNA upon oxidative stress, impaired translation, lower intracellular protein content, and decreased cell growth rate were found. Our data demonstrate that APE1 affects cell growth by directly acting on RNA quality control mechanisms, thus affecting gene expression through posttranscriptional mechanisms.

Genome-wide analysis and proteomic studies reveal APE1/Ref-1 multifunctional role in mammalian cells.

Apurinic apyrimidinic endonuclease/redox effector factor 1 (APE1/Ref-1) protects cells from oxidative stress by acting as a central enzyme in base excision repair pathways of DNA lesions and through its independent activity as a redox transcriptional co-activator. Dysregulation of this protein has been associated with cancer development. At present, contrasting data have been published regarding the biological relevance of the two functions as well as the molecular mechanisms involved. Here, we combined both mRNA expression profiling and proteomic analysis to determine the molecular changes associated with APE1 loss-of-expression induced by siRNA technology. This approach identified a role of APE1 in cell growth, apoptosis, intracellular redox state, mitochondrial function, and cytoskeletal structure. Overall, our data show that APE1 acts as a hub in coordinating different and vital functions in mammalian cells, highlighting the molecular determinants of the multifunctional nature of APE1 protein.

APE1/Ref-1 regulates PTEN expression mediated by Egr-1.

APE1/Ref-1, the mammalian ortholog of E. coli Xth, and a multifunctional protein possessing both DNA repair and transcriptional regulatory activities, has dual role in controlling cellular response to oxidative stress. It is rate-limiting in repair of oxidative DNA damage including strand breaks and also has co-transcriptional activity by modulating genes expression directly regulated by Egr-1 and p53 transcription factors. PTEN, a phosphoinositide phosphatase, acts as an 'off' switch in the PI-3 kinase/Akt signalling pathway and regulates cell growth and survival. It is shown here that transient alteration in the APE1 level in HeLa cells modulates PTEN expression and that acetylatable APE1 is required for the activation of the PTEN gene. Acetylation of APE1 enhances its binding to distinct trans-acting complexes involved in activation or repression. The acetylated protein is deacetylated in vivo by histone deacetylases. It was found that exposure of HeLa cells to H(2)O(2) and to histone deacetylase inhibitors increases acetylation of APE1 and induction of PTEN. The absence of such induction in APE1-downregulated HeLa cells confirmed APE1's role in regulating inducible PTEN expression. That APE1-dependent PTEN expression is mediated by Egr-1 was supported by experiments with cells ectopically expressing Egr-1. Thus, the data open new perspectives in the comprehension of the many functions exerted by APE1 in controlling cell response to oxidative stress.

Bilirubin-induced cell toxicity involves PTEN activation through an APE1/Ref-1-dependent pathway.

Unconjugated bilirubin (UCB) is the major degradation product of the heme catabolism. A growing body of evidences suggests that UCB plays major biological effects by inhibiting cell proliferation in cancer cell lines and eliciting cell toxicity particularly in neurons and glial cells. Early molecular events responsible for bilirubin-induced cytotoxicity remain poorly understood. Using HeLa cells and mouse embryonic fibroblasts, we found that UCB at a concentration of free pigment (Bf) of 80 nM induced oxidative stress, promoting a significant increase in intracellular reactive oxygen species (ROS) and a decreased cell survival (by the MTT test). The ROS increase activated the antioxidant cell response through APE1/Ref-1, a master redox regulator in eukaryotic cells. Activation of APE1/Ref-1 was followed by a concomitant activation of Egr-1 transcription factor and by an upregulation of PTEN tumor suppressor, an Egr-1 target gene, leading to inhibition of cell growth. Blocking ROS generation with N-acetylcysteine pretreatment, restored cell survival, limited the upregulation of PTEN in response to UCB, and prevented the inhibition of cell proliferation. HeLa cells transfected with mutants of the PTEN promoter or silenced with APE1/Ref-1 small interference RNA confirmed that UCB modulates a signaling pathway involving APE1/Ref-1, Egr-1, and PTEN. These findings describe a new molecular pathway involved in the cytotoxic effects of UCB.

Altered intracellular redox status in Gaucher disease fibroblasts and impairment of adaptive response against oxidative stress.

Gaucher disease (GD) is a lysosomal storage disorder, due to glucosylceramide (GlcCer) accumulation in several body tissues, which causes cellular failure by yet unidentified mechanisms. Several evidence indicates that GD pathogenesis is associated to an impairment in intracellular redox state. In fibroblast primary cultures, reactive oxygen species (ROS) levels and protein carbonyl content resulted significantly increased in GD patients compared to healthy donors, suggesting that GD cells, facing a condition of chronic oxidative stress, have evolved an adaptive response to survive. The ROS rise is probably due to NAD(P)H oxidase activity, being inhibited by the treatment with diphenylene iodonium chloride. Interestingly, GD cells are more sensitive to H(2)O(2) induced cell death, suggesting a dysregulation in the adaptive response to oxidative stress in which APE1/Ref-1 plays a central role. We found that the cytoplasmic amounts of APE1/Ref-1 protein were significantly higher in GD fibroblasts with respect to controls, and that GD cells failed to upregulate its expression upon H(2)O(2) treatment. Both ROS and APE1/Ref-1 increases are due to GlcCer accumulation, being prevented by treatment of GD fibroblasts with Cerezyme and induced in healthy fibroblasts treated with conduritol-beta-epoxide. These data, suggesting that GD cells display an impairment in the cellular redox state and in the adaptive cellular response to oxidative stress, may open new perspectives in the comprehension of GD pathogenesis.

Bisphosphonates activate nucleotide receptors signaling and induce the expression of Hsp90 in osteoblast-like cell lines.

Bisphosphonates are the most important drugs used in the treatment of osteoporosis as they inhibit osteoclast resorption and stimulate proliferation of osteoblasts. However, the molecular mechanisms responsible for these effects are still poorly elucidated. It is known that nucleotide receptors-mediated signaling plays a central role in modulating osteoblasts growth in response to mechanical stress. By using osteoblast-like cell lines (i.e., HOBIT, MG-63, ROS P2Y), which express P2Y receptors, we found that the treatment with risedronate promotes non-lytic ATP release leading to activation of ERKs through the involvement of P2Y receptors triggering. A major role in this signal transduction pathway seems to be the involvement of P2Y(1) and P2Y(2) receptors, since the stimulatory effect of risedronate on ERKs is not appreciable in ROS 17/2.8 cells, which do not express these two receptors. Differential proteomics analysis identified Hsp90 upregulation as a result of risedronate effect on HOBIT and MG-63 cells. The stimulatory effect is dependent on ERKs activation involving nucleotide receptors triggering and leads to increased proliferation of osteoblast-like cells. In fact, functional inactivation of Hsp90 by the specific inhibitor 17-AAG prevents the bisphosphonate-induced mitogenic effects in osteoblasts. These findings show that bisphosphonates, by inducing ATP release, may also act through nucleotide receptors signaling leading to ERKs activation and may exert their mitogenic role on osteoblasts through the involvement of Hsp90.

Identification and functional characterization of five novel mutant alleles in 58 Italian patients with Gaucher disease type 1.

Gaucher disease (GD) is the most frequent lysosomal glycolipid storage disorder due to an autosomal recessive deficiency of acid beta-glucosidase characterized by the accumulation of glucocerebroside. In this work we carried out the molecular analysis of the glucocerebrosidase gene (GBA) in 58 unrelated patients with GD type 1. We identified five novel genetic alterations: three missense changes c.187G>A (p.D63N), c.473T>G (p.I158S), c.689T>A (p.V230E), a gene-pseudogene recombinant allele and a non-pseudogene-derived complex allele [c.1379G>A;c.1469A>G] encoding [p.G460D;p.H490R]. All mutant alleles were present as compound heterozygotes in association with c.1226A>G (p.N409S), the most common mutation in GD1. The missense mutant proteins were expressed in vitro in COS-1 cells and analyzed by enzyme activity, protein processing and intracellular localization. Functional studies also included the c.662C>T (p.P221L) mutation recently reported in the Spanish GD population (Montfort et al., 2004). The missense mutant alleles retained an extremely low residual enzyme activity with respect to wild type; the complex allele expressed no activity. Processing of the mutant proteins was unaltered except for c.473T>G which was differently glycosylated due to the exposition of an additional glycosylation site. Immunofluorescence studies showed that protein trafficking into the lysosomes was unaffected in all cases. Finally, the characterization of the novel recombinant allele identified a crossover involving the GBA gene and pseudogene between intron 5 and exon 7.

Glycogenosis type II: identification and expression of three novel mutations in the acid alpha-glucosidase gene causing the infantile form of the disease.

Glycogenosis type II (GSDII) is an autosomal recessive disorder due to the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). We identified three novel point mutations, C399A, T1064C, and C2104T, in three unrelated Italian patients with the infantile form of the disease. The C399A mutation was present in homozygosity in proband 1. The C >A transition introduces a premature stop signal in exon 2 resulting in no enzyme production that is correlated with the severe clinical phenotype in this patient. The other two nucleotide changes were missense mutations. The T1064C mutation, which changes Leu in position 355 into Pro, was carried in homozygosity by proband 2. The C2104T nucleotide change, which substitutes Arg 702 into Cys, was present in proband 3 in combination with a known severe mutation DeltaI17-18. The in vitro expression in COS-1 cells of T1064C and C2104T constructs demonstrated no enzymatic activity with respect to the negative control cells. Western blot analysis revealed that both T1064C and C2104T mutant proteins produced in COS-1 cells migrated in SDS-PAGE as the GAA inactive precursor of 110kDa. Immunofluorescence detection of mutant alpha-glucosidases showed enzyme localization primarily in the ER-Golgi compartment, suggesting that T1064C and C2104T mutations could affect the normal processing and stability of the enzyme. In vitro studies demonstrated that the same degree of deficiency in T1064C and C2104T mutations, which is in contrast with patient phenotype. A better correlation was observed with the in vivo studies since proband 2, with a less severe phenotype, presented with low residual enzyme activity while in proband 3, with a classic severe infantile onset GSDII, fibroblast enzyme activity was completely absent.

Identification of four novel mutations in the alpha glucosidase gene in five Italian patients with infantile onset glycogen storage disease type II.

Glycogen storage disease type II (GSDII) is an autosomal recessive disorder due to the deficiency of the lysosomal enzyme acid alpha glucosidase. Four novel mutations (C670T, G989A, G2188T, and Delta 23 nt 828-850) were identified in five Italian patients with the infantile form of the disease. The C670T mutation was present in two unrelated patients in heterozygosity; the effect on enzyme activity was assessed by in vitro expression. COS-1 cells expressing the C670T allele had a twofold higher activity than the negative control cells. The G989A and G2188T point mutations lead to the introduction of premature stop signals that results in truncated forms of alpha glucosidase. The in vitro expression of G2188T allele demonstrated no increment in activity compared to negative control. The frame shifting deletion of nucleotides 828-850 was identified in one patient in heterozygosity. The shift in the reading frame introduces a stop codon 135 nucleotides downstream the deletion junction that results in a truncated protein without catalytic activity. Nested PCR screening showed that the mutation was carried by the mother and was absent in the other members of the family. The four novel severe mutations herein described concerned only infantile onset GSDII patients; the loss of enzyme activity is correlated with the severity of the disease.